The drive shaft is situated at the end of a motor unit, and the cutter head of the keratome is releasably fixed thereto. The finger projects into the sliding housing for the blade so as to reach a coupling groove of the blade (or its support) and be received therein.
Perpendicularly to the motion of the blade, the housing provided in the head possesses a section that is substantially identical to the section of the blade and support assembly which slides therein, ignoring operating clearance. This housing passes through the head, and the blade is slid into the housing through one of its ends prior to the head being assembled to the motor unit. It is only after the head has been assembled on the motor unit that the drive finger holds the blade in said housing by penetrating into the groove.
It is a drawback to need to take care to keep the blade present inside the housing of the head until it has been assembled onto the motor unit, particularly since it is necessary to manipulate the head while it is being assembled, and it is at this time that the blade might escape from its housing if care is not taken.
It is also a drawback to have no control over the position of the blade inside the housing of the head at the time it is being mounted on the motor unit. The volume swept by the drive finger while it is rotating is relatively small (the reciprocating stroke of the blade has a peak-to-peak amplitude of about 1 millimeter), such that the groove in the blade might not intersect this volume, and as a result when the finger is put into rotation co-operation between the finger and the groove does not occur.